When a sanitary fitting, either a tap, a mixer or a shower mixer for example, feeds a water outlet equipped with a flexible, usually ended with a small shower, one should provide a device which, if the small shower is immersed in the pool full of water and if a depression occurs in one of the water inlet pipe, prevent the water in the pool from being sucked up into the distributing water circuit.
One knows such a backflow preventing device thanks to the document DE-A1-3603503 which comprises, mounted in a chamber connected to the water pipe coming out of the framework, a flexible tube feeding the small shower and to the open air, a shutter which closes normally the exhaust to the open air of this small shower and which connects the water outlet with the flexible tube. This shutter may displace itself against its own weight so that when a depression occurs in the water outlet of the framework, the shutter is released and provokes the communication of this chamber with the open air.
This backflow preventing device presents a major drawback in that the closing strength of the shutter is the gravity. Indeed, this shutter should mandatorily be mounted in such a way that it could displace itself along a vertical axis. Thus, when it is integrated into the body of the sanitary framework, which is generally the case, this framework may no longer be indiscriminately fastened on a horizontal work plane or on a vertical wall. It is then necessary to provide different frameworks according to their purpose.
Furthermore, the depression needed to provoke the opening of the backflow preventing device is not acurately determined because it depends on one hand on the weight of the shutter and also on the other hand on the adjustment of the O-ring joint into a boring. This strength due to the friction of the strength necessary to the displacement of the shutter is undetermined and varies over time due to limestone fouling of the device and also due to the O-ring joint ageing.
One also knows from document EP-A1-0.495,372 a backflow preventing device for sanitary fittings which should also be mounted vertically, both ball-shaped closing members, serially mounted, being able to move themselves under the action of their own weight. Furthermore, this device must mandatorily receive the water delivered by the tap or the mixer axially, this water slipping out normally toward the neck through radial holes giving access to an output channel in the framework. The air intake is also mandatorily axially located under the second ball. This device is complex and is liable to block itself due to limestone fouling and it can only be mounted in a position determined by the gravity action on the balls in the framework.
From the document EP-B1-0.370.281, one knows a backflow preventing device for sanitary framework which also comprises a chamber connected to the water outlet of the framework, to the flexible tube feeding the small shower and to the open air in which moves a shutter allowing the connection to the open air of either the chamber, or the water outlet of the framework. This shutter is composed of a bellowed membrane fastened by its perimeter to the wall of the chamber and displacing itself under the effect of the pressure or the depression coming from the water outlet of the sanitary framework. Moreover, the ageing of the membrane as well as the effect of the limestone deposit modifies its suppleness and thus the strength necessary for its displacement.
Lastly, one knows thanks to the document EP-A2-0.999.914 a backflow preventing device working on the Venturi or water pump principle. This also implies a particular arrangement of the water inlet and outlet which restricts and complicates the production of the sanitary fitting body.